1. Field of the Invention
The present invention relates to a method of producing a dielectric ceramic composition used, for example, as a dielectric layer of a multi-layer ceramic capacitor and a method of producing an electronic device using the dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
A multi-layer ceramic capacitor as an example of electronic devices is formed by printing a conductive paste on a green sheet comprised of a predetermined dielectric ceramic composition, stacking a plurality of green sheets printed the conductive paste thereon and being fired the green sheet and internal electrodes as one body.
A dielectric ceramic composition had a characteristic that it is reduced and becomes semiconductive when fired in a neutral or reducing atmosphere having a low oxygen partial pressure. Therefore, when producing a multi-layer ceramic capacitor, it was inevitable to fire in an oxidizing atmosphere having a high oxygen partial pressure. Accordingly, as an internal electrode material to be fired at a time with the dielectric ceramic composition, it is necessary to use an expensive noble metal, such as palladium and platinum, which does not melt at a temperature the dielectric ceramic composition sinters and is not oxidized when being fired in the oxidizing atmosphere, so it has been a large obstacle for lowering the cost of the multi-layer ceramic capacitor to be produced.
On the other hand, to use an inexpensive base metal, such as nickel and copper, as an internal electrode material, it is necessary to develop a dielectric ceramic composition having characteristics of not becoming semiconductive by being fired at a low temperature in a neutral or reducing atmosphere, that is having excellent resistance to reducing, showing sufficient dielectric constant and excellent dielectric characteristics (for example, having a small capacity-temperature change rate) after firing.
A variety of proposals have been made for dielectric ceramic composition wherein a base metal can be used as an internal electrode material in the related art.
For example, The Japanese Unexamined Patent Publication No. 1988-224108 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr1xe2x88x92xCax)m(Ti1xe2x88x92yZry)O3 (note that 0.30xe2x89xa6xxe2x89xa60.50, 0.03xe2x89xa6yxe2x89xa60.20, 0.95xe2x89xa6mxe2x89xa61.08) and containing as subcomponents Mn (converted to MnO2) for 0.01 to 2.00 parts by weight and SiO2 for 0.10 to 4.00 parts by weight with respect to 100 parts by weight of the main component.
The Japanese unexamined Patent Publication No. 1988-224109 discloses a dielectric ceramic composition further containing ZnO for 0.01 to 1.00 parts by weight with respect to the above main component in addition to the above Mn and SiO2.
The Japanese Unexamined Patent Publication No. 1992-206109 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr1xe2x88x92xCax)m(Ti1xe2x88x92yZry)O3 (note that 0.30xe2x89xa6xxe2x89xa60.50, 0.00xe2x89xa6yxe2x89xa60.20, 0.95xe2x89xa6mxe2x89xa61.08) and the particle diameter is made to be in the range of 0.1 to 1.0 xcexcm.
The Japanese Examined Patent Publication No. 1987-24388 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by MeOkTiO2 (note that Me is a metal selected from Sr, Ca and Sr+Ca, and k is 1.00 to 1.04) and 0.2 to 10.0 parts by weight of a glass component with respect to 100 parts by weight of the main component wherein Li2O, M (note that M is at least one kind of metal oxide selected from BaO, CaO and SrO) and SiO2 are used at a predetermined mole ratio.
The Japanese Unexamined Patent Publication No. 1984-227769 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by {(Sr1xe2x88x92xCax)O}k.TiO2 (note that 0xe2x89xa6xxe2x89xa61.00, 1.00xe2x89xa6kxe2x89xa61.04) and 0.2 to 10.0 parts by weight of a glass component with respect to 100 parts by weight of the main component wherein Li2O, M (note that M is at least one kind of metal oxide selected from BaO, CaO and SrO) and SiO2 are used at a predetermined mole ratio.
The Japanese Unexamined Patent Publication No. 1988-224106 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr1xe2x88x92xCax)m(Ti1xe2x88x92yZry)O3 (note that 0.30xe2x89xa6xxe2x89xa60.50, 0.03xe2x89xa6yxe2x89xa60.20, 0.95xe2x89xa6mxe2x89xa61.08) and containing as a subcomponent 0.01 to 2.00 parts by weight of Mn (converted to MnO2), 0.10 to 4.00 parts by weight of SiO2 and 0.01 to 1.00 parts by weight of Mo (converted to MoO) with respect to 100 parts by weight of the main component.
The Japanese Unexamined Patent Publication No. 1992-14704 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (SrxCa1xe2x88x92x)(ZryTi1xe2x88x92y)O3 (note that 0.59xe2x89xa6xxe2x89xa60.65, 0xe2x89xa6yxe2x89xa60.1) and containing less than 3.0 parts by weight of SiO2 (note that 0 parts by weight is not included) with respect to 100 parts by weight of the main component.
However, there have been disadvantages in the dielectric ceramic compositions described in the publications that insulation resistance (IR) is liable to decline particularly when made to be a thin film, and when producing a multi-layer ceramic capacitor having a base metal internal electrode by using the dielectric ceramic composition, an defect rate of an initial insulation resistance of an obtained multi-layer ceramic capacitor increases.
An object of the present invention is to provide a method of producing a dielectric ceramic composition, having excellent resistance to reducing during firing and excellent capacity-temperature characteristics after firing, and a method of producing an electronic device, such as a chip capacitor wherein the insulation resistance is hard to be deteriorated particularly when made to be a thin layer and an defect rate of the initial insulation resistance is low.
To attain the above object, according to a first aspect of the present invention, there is provided a method of producing a dielectric ceramic composition containing a main component expressed by a composition formula of (AO)m.BO2, wherein the element A in said composition formula is at least one element selected from Sr, Ca and Ba, and the element B in said composition formula is at least one element selected from Ti and Zr,
characterized by producing the dielectric ceramic composition by using a source material expressed by a composition formula of (AO)mxe2x80x2.BO2, wherein the mole ratio mxe2x80x2 in said composition formula fulfills mxe2x80x2 less than m.
Preferably, said dielectric ceramic composition is produced by firing after adding to said source material a substance containing said element A. More preferably, said dielectric ceramic composition is produced by firing after adding to said source material a substance containing said element A, without adding a substance containing said element B.
To attain the above object, particularly preferable embodiment is a method of producing a dielectric ceramic composition according to the second aspect of the present invention below.
According to the second aspect of the present invention, there is provided a method of producing a dielectric ceramic composition containing a main component expressed by a composition formula of {(Sr1xe2x88x92xCax)O}m.(Ti1xe2x88x92yZry)O2 wherein the code x in said composition formula fulfills 0xe2x89xa6xxe2x89xa61.00 and the code y in said composition formula fulfills 0xe2x89xa6yxe2x89xa60.20,
characterized by producing the dielectric ceramic composition by using a source material expressed by a composition formula of { (Sr1xe2x88x92xCax)O}mxe2x80x2.(Ti1xe2x88x92yZry)O2, wherein the mole ratio mxe2x80x2 in said composition formula fulfills mxe2x80x2 less than m.
Preferably, said dielectric ceramic composition is produced by firing after adding to said source material a substance containing at least one element of said Sr and Ca. More preferably, said dielectric ceramic composition is produced by firing after adding to said source material a substance containing at least one element of said Sr and Ca, without adding a substance containing Ti.
Preferably, relationship of the mole ratios m and mxe2x80x2 in said composition formula fulfills mxe2x88x92mxe2x80x2 less than 0.085.
Preferably, the mole ratio m in the composition formula in the main component of said dielectric ceramic composition fulfills 0.94 less than m less than 1.08.
To attain the above object, according to the first aspect of the present invention, there is provided a method of producing an electronic device comprising a dielectric layer includes a dielectric ceramic composition containing a main component expressed by a composition formula of (AO)m.BO2, wherein the element A in said composition formula is at least one element selected from Sr, Ca and Ba, and the element B in said composition formula is at least one element selected from Ti and Zr,
characterized by producing said dielectric ceramic composition by using a material expressed by a composition formula of (AO)mxe2x80x2.BO2, wherein the mole ratio mxe2x80x2 in said composition formula fulfills mxe2x80x2 less than m.
To attain the above object, particularly preferable embodiment is a method of producing an electronic device according to the second aspect of the present invention below.
According to the second aspect of the present invention, there is provided a method of producing an electronic device comprising a dielectric layer includes a dielectric ceramic composition containing a main component expressed by a composition formula of {(Sr1xe2x88x92xCax)O}m.(Ti1xe2x88x92yZry)O2, wherein the code x in said composition formula fulfills 0xe2x89xa6xxe2x89xa61.00 and the code y in said composition formula fulfills 0xe2x89xa6yxe2x89xa60.20,
characterized by producing said dielectric ceramic composition by using a source material expressed by a composition formula of {(Sr1xe2x88x92xCax)O}mxe2x80x2.(Ti1xe2x88x92yZry)O2, wherein the mole ratio mxe2x80x2 in said composition formula fulfills mxe2x80x2 less than m.
It has been made clear by the present inventors that an insulation resistance error occurs when producing a dielectric ceramic composition containing a main component expressed by the composition formula of (AO)m.BO2 and especially when it is made to be a thin film. Causes thereof are not always clear, but it is considered that a segregation phase wherein an element B becomes rich in the dielectric ceramic composition after firing and that the insulation resistance and a dielectric constant of the dielectric decline.
In a method of producing a dielectric ceramic composition according to the first aspect of the present invention, it is possible to produce a dielectric ceramic composition having a high resistance to reducing during firing and excellent capacity-temperature characteristics after firing, wherein insulation resistance is hard to decline when it is made to be a thin layer of, for example, about 4 xcexcm by producing the above dielectric ceramic composition by using the material expressed by the composition formula of (AO)mxe2x80x2.BO2 having a smaller mole ratio mxe2x80x2 than a mole ratio m after firing. By using the material satisfying mxe2x80x2 less than m, an element B is not necessarily added thereafter before firing and it is considered that the above element B can prevent generation of a rich segregation phase.
In a method of producing a dielectric ceramic composition according to the second aspect of the present invention, by producing the above dielectric ceramic composition by using a material expressed by a composition formula of {(Sr1xe2x88x92xCax)O}mxe2x80x2.(Ti1xe2x88x92yZry)O2 having a smaller mole ratio mxe2x80x2 than a mole ratio m after firing, the element B can prevent generation of a rich segregation phase due to the same reason, accordingly, a dielectric ceramic composition having a high resistance to reducing during firing and excellent capacity-temperature characteristics after firing, wherein an insulation resistance is hard to decline when it is made to be a thin layer of, for example, about 4 xcexcm, can be produced. The above facts are found by the present inventors for the first time.
By a method of producing an electronic device according to the first and second aspects of the present invention, an electronic device like a chip capacitor, etc. in which an defect rate of an initial insulation resistance is small can be produced.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-93416 (filed on March 30), the disclosure of which is expressly incorporated herein by reference in its entirety.